Tension estimation device, life evaluation device, and robot system

The present invention relates to a tension estimation device, a life evaluation device, and a robot system.

Patent Document 1: Japanese Unexamined Patent Application, Publication No. 2020-8472 In a robot, it is important to estimate life of a drive system of the robot and foresee a breakdown before the robot breaks down. For example, a technique is disclosed in Patent Document 1 in which temperatures of components of a robot are estimated and life of the components is estimated with high accuracy.

There have been known multi-axis robots such as a vertical multi-joint robot including a transmission mechanism that transmits power of a motor to a movable portion through a belt. In the robot in which the belt is provided in the transmission mechanism, when temperatures of members constituting the robot rises due to behavior of the robot, the members (mainly cast metal or the like) expand, and thus an inter-axis distance of the belt increases. As a result, tension of the belt increases, which may shorten the life of the drive system including the transmission mechanism. Therefore, in a machine including the transmission mechanism that transmits the power of the motor to the movable portion through the belt, it is necessary to estimate the life of the drive system in consideration of changes in tension of the belt due to the behavior.

Therefore, it is desirable to provide a tension estimation device capable of estimating the tension of the belt with high accuracy, a life evaluation device capable of estimating the life of the transmission mechanism with high accuracy from the tension of the belt, and a robot system.

A tension estimation device according to an aspect of the present disclosure includes: a transmission mechanism that transmits power through a belt; at least one motor disposed close to the belt; a motor heating value calculation unit that calculates a motor heating value based on at least one of a current value and a rotation speed of the at least one motor; a friction heating value calculation unit that calculates a friction heating value of the transmission mechanism, based on at least one of the current value and the rotation speed of the at least one motor and a friction coefficients of at least one axis disposed close to the belt; and a belt tension estimation unit that estimates tension of the belt based on the motor heating value and the friction heating value.

A life evaluation device according to an aspect of the present disclosure includes: the tension estimation device; and a life estimation unit that estimates life of the transmission mechanism based on the tension of the belt estimated by the tension estimation device.

A robot system according to an aspect of the present disclosure includes: a robot including a plurality of motors, a plurality of movable portions, and one or more transmission mechanisms that transmit power of at least one of the plurality of motors to the plurality of movable portions through a belt; a control device that controls the plurality of motors of the robot; and the life evaluation device.

According to aspects of the present disclosure, it is possible to provide a tension estimation device capable of estimating tension of a belt with high accuracy, a life evaluation device capable of estimating life of a transmission mechanism with high accuracy from the tension of the belt, and a robot system including the tension estimation device and the life evaluation device.

1 FIG. 1 2 3 2 4 3 Embodiments of a tension estimation device, a life evaluation device, and a robot system of the present disclosure will be described in detail below with reference to the drawings. As shown in, a robot systemincludes a robot, a robot controllerthat controls the robot, and a display unitconnected to the robot controller.

2 2 2 2 2 2 2 2 2 21 22 21 23 22 24 23 25 24 26 25 a b c d e f The robotof the present embodiment is a vertical multi-joint robot including a plurality of movable portions. Specifically, the robotis a 6-axis vertical multi-joint robot including 6 axes of a J1 axis, a J2 axis, a J3 axis, a J4 axis, a J5 axis, and a J6 axisas movable portions. The robotincludes a base portioninstalled on a floor surface or the like, a first turning portionprovided on the base portion, a first arm portionattached to the first turning portion, a second turning portionattached to the first arm portion, a second arm portionattached to the second turning portion, and a wrist unitattached to a tip of the second arm portion.

22 2 21 23 2 22 24 2 23 25 25 2 24 26 2 25 2 2 a b c d e e f. The first turning portionis rotatable in a horizontal direction by the J1 axiswith respect to the base portion. The first arm portionis swingable in a front-rear direction by the J2 axiswith respect to the first turning portion. The second turning portionis swingable in an up-down direction by the J3 axiswith respect to the first arm portion. The second arm portionis rotatable around an axis along a longitudinal direction of the second arm portionby the J4 axiswith respect to the second turning portion. The wrist unitis swingable in an up-down direction by the J5 axiswith respect to the second arm portion, and is rotatable around an axis intersecting the J5 axisby the J6 axis

2 2 2 25 2 25 5 26 2 5 2 6 1 FIG. 2 FIG. a f e e The robotis provided, on the axes, with motors (not shown in) for driving the axes (J1 axisto J6 axis) and transmission mechanisms that transmit power of the motors to the axes. For example,shows the inside of the second arm portionof the robot. Inside the second arm portion, a J5 axis motoris disposed to swing the wrist unitaround the J5 axis. Power of the J5 axis motoris transmitted to the J5 axisvia the transmission mechanism.

6 61 5 5 62 2 63 61 62 64 62 5 2 6 a e a e The transmission mechanismincludes a first pulleyattached to an output axisof the J5 axis motor, a second pulleyattached to the J5 axis, a beltbridged between the first pulleyand the second pulley, and a deceleratorthat decelerates a rotation of the second pulley. The output axisand the J5 axisare rotatably supported by bearings (not shown), respectively. These bearings (not shown) in the transmission mechanismare members, a life of which changes according to a change in tension of the belt.

2 FIG. 1 FIG. 25 7 5 2 7 2 24 8 2 f f d. As shown in, inside the second arm portion, a J6 axis motoris also provided close to the J5 axis motorto drive the J6 axis. Power of the J6 axis motoris transmitted to the J6 axisvia a transmission mechanism (not shown). Further, as shown in, the second turning portionis provided with a J4 axis motorto drive a fourth axis

2 6 25 6 25 25 2 25 5 5 2 63 61 62 6 2 FIG. 2 FIG. a e The life of the transmission mechanism provided in the robotis affected by a temperature of a component site where the transmission mechanism is disposed. For example, in the case of the transmission mechanismprovided inside the second arm portionshown in, the life of the transmission mechanismis affected by the temperature of the second arm portionitself. In other words, when the temperature of the second arm portionrises due to the driving of the robot, a member (mainly cast metal or the like) constituting the second arm portionexpands, and an inter-axis distance L between the output axisof the J5 axis motorand the J5 axisshown inincreases. Accordingly, tension of the beltbecomes larger, and a load on the first pulleyand the second pulleyincreases. As a result, the life of the transmission mechanismis reduced.

2 25 2 25 5 25 7 2 2 2 2 63 6 25 6 63 f d e f The temperature rise in the component site of the robotcan be caused due to not only heat generated from the motor disposed inside the component site, but also heat generated from another component site disposed close to the component site. For example, in the second arm portionshown in FIG., the temperature rise of the second arm portioncan be caused due to not only heat generated from the J5 axis motordisposed inside the second arm portion, but also heat generated from the J6 axis motorfor driving the J6 axisand frictional heat generated by behavior of each of the J4 axis, the J5 axis, and the J6 axiswhich are friction sites. Therefore, when a user wants to estimate the tension of the beltof the transmission mechanismprovided in the second arm portionand the life of the transmission mechanism, it is also necessary to consider the heat generated from these component sites disposed close to the belt.

3 2 2 3 31 2 32 63 6 2 33 6 2 The robot controlleris electrically connected to the robotand comprehensively controls the behavior of the robot. The robot controllerincludes a control devicethat controls respective portions such as motors of the robot, a tension estimation devicethat estimates the tension of the beltprovided at the transmission mechanismof the robot, and a life evaluation devicethat estimates the life of the transmission mechanismof the robot.

4 4 3 3 The display unitis configured by a liquid crystal display screen, for example. The display unitis connected to the robot controllerin a wired or wireless manner, and display various information transmitted from the robot controlleron the screen.

32 33 3 32 321 322 323 324 3 FIG. 3 FIG. Next, the tension estimation deviceand the life evaluation deviceprovided in the robot controllerwill be described with reference to. As shown in, the tension estimation deviceincludes a motor heating value calculation unit, a friction heating value calculation unit, an air-cooling radiation amount calculation unit, and a belt tension estimation unit.

321 31 31 321 31 3 FIG. The motor heating value calculation unitcalculates a motor heating value based on a state quantity of the motor input from the control device. The control deviceinputs, to the motor heating value calculation unit, at least one of a motor current value and a motor rotation speed of at least one motor disposed close to the belt, which is a target for tension estimation. As shown in, the present embodiment is configured in which both the motor current value and the motor rotation speed are input from the control device.

25 2 5 7 63 63 5 7 63 25 5 7 321 2 FIG. The motor disposed close to the belt is a motor disposed close enough to the belt that the heat generated by driving of the motor affects the tension of the belt. For example, in the case of the second arm portionof the robotshown in, the J5 axis motorand the J6 axis motorare disposed close to the belt. The tension of the beltis affected by heat generated by the J5 axis motorand the J6 axis motor. Therefore, in a case of estimating the tension of the beltof the second arm portion, at least one of motor current values and motor rotation speeds of the J5 axis motorand the J6 axis motoris input to the motor heating value calculation unit.

321 M =a×C +b×V +c V n n n n 2 where, n M: motor heating value of Jn axis motor [W], n C: motor current value of Jn axis motor [Ap], n V: motor rotation speed of Jn axis motor [rpm], and a, b, c: coefficients The motor heating value calculation unitcalculates, based on at least one of the motor current value and the motor rotation speed to be input, a motor heating value of a motor that drives an axis, which is a target for calculation, using Formula (1) below.×()  (1)

322 31 322 25 2 322 5 7 25 2 2 2 2 63 2 FIG. 2 FIG. d e f The friction heating value calculation unitcalculates a friction heating value in the transmission mechanism, based on at least one of the motor current value input from the control device, the motor rotation speed, and the friction coefficient of at least one axis disposed close to the belt which is a target for tension estimation. The motor current value and the motor rotation speed input to the friction heating value calculation unitare the motor current value and the motor rotation speed of at least one motor disposed close to the belt which is the target for tension estimation. For example, in the case of the second arm portionof the robotshown in, the motor current value and the motor rotation speed input to the friction heating value calculation unitare the motor current value and the motor rotation speed of the J5 axis motorand the J6 axis motor. The axis is a site that generates frictional heat due to driving. For example, in the case of the second arm portionof the robotshown in, frictional heat generated by driving of the J4 axis, the J5 axis, and the J6 axismay affect the tension of the belt.

3 FIG. 322 31 31 322 F =k ×C V +k ×V +k V n 1 n n 2 n 3 n 2 where, n F: friction heating value of axis to be driven by Jn axis motor [W], n C: motor current value of Jn axis motor [Ap], n V: motor rotation speed of Jn axis motor [rpm], and k: friction coefficient. As shown in, at least one of the motor current value, the motor rotation speed, and the friction coefficient of the axis is input to the friction heating value calculation unitfrom the control device. The friction coefficient of the axis is a unique value for each axis, and is stored in advance in a storage unit (not shown) of the control deviceas a value for each axis. The friction heating value calculation unitcalculates a friction heating value in the transmission mechanism using Formula (2) below, based on at least one of the motor current value, the motor rotation speed, and the friction coefficient.×()  (2)

323 2 2 2 2 wcp wcp wcp a f. V The air-cooling radiation amount calculation unitcalculates an air-cooling radiation amount of the transmission mechanism based on the moving speed of the transmission mechanism. The air-cooling radiation amount is a radiation amount generated due to a relative speed with surrounding air when the arm portion moves in air due to the behavior of the robot. The air-cooling radiation amount is proportional to a moving speed rate (V) of the transmission mechanism. The moving speed rate (V) of the transmission mechanism is calculated by Formula (3) below. In the robot, the speed of the arm portion is uniquely determined from the amount of minute angle change of the J1 axisto the J6 axis=(Speed at specific position of arm portion)/(Maximum speed at specific position of arm portion)  (3)

324 321 322 323 2 0 The belt tension estimation unitcalculate the tension of the belt in the transmission mechanism using a belt tension estimation formula indicated by Formula (4) below, based on the motor heating value calculated by the motor heating value calculation unit, the friction heating value calculated by the friction heating value calculation unit, and the air-cooling radiation amount calculated by the air-cooling radiation amount calculation unit. Here, Tand a, b, c, and d indicate model-specific coefficients that do not depend on the movement of the robot.

where, T: estimated tension of belt, 0 T: initial tension of belt, n F: friction heating value of an axis to be driven by Jn axis motor [W], n M: motor heating value of Jn axis motor [W], wcp V: moving speed rate of transmission mechanism, m: any combinatorial integer, and a, b, c, d: coefficients.

2 63 6 25 5 7 63 2 2 2 63 5 7 2 2 2 d e f d e f In the robot, for example, the tension of the beltof the transmission mechanismof the second arm portionis affected by the motor heating values of the J5 axis motorand the J6 axis motordisposed close to the beltand the frictional heating values of the J4 axis, J5 axis, and the J6 axiswhich are the axes disposed close to the belt. Therefore, in this case, the motor heating values of the J5 axis motorand the J6 axis motorare used as the motor heating value M, and the frictional heating values of the J4 axis, J5 axis, and the J6 axisare used as the friction heating value F in formula (4) above.

63 6 25 2 Here, a description will be given with respect to a case of estimating the tension of the beltof the transmission mechanismin the second arm portionwhen the robotperforms the following behavior.

TABLE 1 J4 AXIS J5 AXIS J6 AXIS n MOTOR CURRENT VALUE C[Ap] 10 12.5 7.5 n MOTOR ROTATION SPEED V[rpm] 1500 1500 1500

2 5 2 7 2 5 5 6 6 e f In such behavior of the robot, when a=0.5, b=0.005, and c=0.000005, a motor heating value Mof the J5 axis motorfor driving the J5 axisis 25 [W] (M=25 [W]) and a motor heating value Mof the J6 axis motorfor driving the J6 axisis 22.5 [W] (M=22.5 [W]), from Formula (1).

2 2 2 2 2 2 d d e e f f a4 b4 c4 4 4 a5 b5 c5 3 5 a6 b6 c6 6 5 In the J4 axis, when a friction coefficient kfor a mean of motor current speeds is 0.005, a friction coefficient kfor a mean of motor rotation speeds is 0.10, and a friction coefficient kfor a square mean value of the motor rotation speed is 0.0001, a friction heating value Fof the J4 axisis 450 [W] (F=450 [W]) from Formula (2). Similarly, in the J5 axis, when a friction coefficient kfor a mean of motor current speeds is 0.0001, a friction coefficient kfor a mean of motor rotation speeds is 0.02, and a friction coefficient kfor a square mean value of the motor rotation speed is 0.00001, a friction heating value Fof the J5 axisis 54.4 [W] (F=54.4 [W]). In the J6 axis, when a friction coefficient kfor a mean of motor current speeds is 0.001, a friction coefficient kfor a mean of motor rotation speeds is 0.08, and a friction coefficient kfor a square mean value of the motor rotation speed is 0.00001, a friction heating value Fof the J6 axisis 153.8 [W] (F=153.8 [W]).

63 63 32 0 1 2 3 4 5 6 5 6 wcp By substitution of these values into Formula (4), the tension T of the beltis obtained. In Formula (4), when T=150 [N], m=4·5·6, m=5~6, m=4·5·6, a=0.1, a=0, a=1.2, b=0.5, b=0.5, c=0.8, d=−0.5, and V=0.1, it is estimated that the tension T of the beltis 200.8 [N] (T=200.8 [N]). Thus, the tension estimation devicecan estimate the tension of the belt with higher accuracy.

0 34 3 34 3 FIG. In the belt tension estimation formula of Formula (4), at least one of the initial tension Tof the belt and the coefficients a, b, c, and d is a parameter that changes with room temperature. Since the belt tension estimation formula includes the parameter that changes with room temperature, the tension of the belt can be estimated in consideration of the room temperature. Therefore, the tension of the belt can be estimated with higher accuracy. The room temperature is input by a room temperature input unitprovided in the robot controller, as shown in. The room temperature may be manually input through the room temperature input unitby an operator, or may be automatically input from a detected value of a temperature sensor (not shown).

0 0 2 2 31 324 2 3 FIG. T′=T −At where, T′: estimated tension of the belt including the change with the lapse of time [N], 0 T: initial tension of the belt [N], A: change with the lapse of time per hour [N/h], and t: operating time [h]. Further, in the belt tension estimation formula of Formula (4), at least one of the initial tension Tof the belt and the coefficients a, b, c, and d may be a parameter that changes with the lapse of time or the operating time of the robot. This is because the tension of the belt may decrease over time. The operating time of the robotis input from the control deviceto the belt tension estimation unit, as shown in. For example, when the decrease in tension of the belt per hour [h] after the robotoperates is defined as A [N/h], estimated tension of the belt including the change with the lapse of time can be calculated by Formula (5) below.  (5)

2 2 2 Thus, coefficients in the belt tension estimation formula of Formula (4) are corrected according to the lapse of time or the operating time of the robot. Therefore, since the belt tension estimation formula includes the parameter that changes with the lapse of time or the operating time of the robot, the tension of the belt can be estimated in consideration of the lapse of time or the operating time of the robot. Therefore, the tension of the belt can be estimated with higher accuracy.

T′=f t T T′: estimated tension of the belt including the change with lapse of time [N], T: estimated tension of the belt [N], and f(t): coefficient dependent on the operating time. Further, the estimated tension of the belt due to the change with lapse of time may be simply calculated by Formula (6) below.()×  (6)where,

3 FIG. 33 32 331 332 333 As shown in, the life evaluation deviceincludes the tension estimation devicedescribed above, and further includes a life estimation unit, a remaining life calculation unit, and a replacement date calculation unit.

331 324 32 6 25 6 63 32 2 FIG. The life estimation unitestimates life of the transmission mechanism based on the estimated tension value estimated by the belt tension estimation unitof the tension estimation device. For example, in the case of the transmission mechanismof the second arm portionshown in, the life of the transmission mechanismis estimated from the estimated tension value of the beltestimated by the tension estimation device.

331 32 331 Generally, it is said that the life of the transmission mechanism is proportional to a cube of the tension of the belt. The life estimation unitestimates the life of the transmission mechanism using Formula (7) below, based on the estimated tension value of the belt obtained by the tension estimation device. For example, in a case of a transmission mechanism of which life reaches 100 [%] in operation for 10000 [h] at tension of the belt being 250 [N], a life progress rate (estimated life value) of the transmission mechanism in operation for 5000 [h] at an estimated tension value of the belt being 200 [N] is 26 [%] from Formula (7) below. Accordingly, the life estimation unitcan estimate that the current life of the transmission mechanism has reached 26%.

where, q S: estimated life value of transmission mechanism [%], T: estimated tension of belt [N], and t: operating time [h].

332 331 33 332 331 r r g S S where, r S: remaining life [%], and g S: estimated life value of transmission mechanism [%]. The remaining life calculation unitcalculates the remaining life of the transmission mechanism based on the estimated life value of the transmission mechanism calculated by the life estimation unit. Accordingly, the life evaluation devicecan notify the operator of the remaining life of the transmission mechanism. Specifically, the remaining life calculation unitcalculates remaining life Sof the transmission mechanism using Formula (8) below, based on the estimated life value of the transmission mechanism calculated by the life estimation unit.=100−[%]  (8)

332 4 4 4 332 332 4 Information on the remaining life calculated by the remaining life calculation unitis sent to the display unitand displayed on the display unit. The display unitmay display the remaining life value itself sent from the remaining life calculation unit, or display a warning when the calculated remaining life value becomes smaller than a preset threshold value. The remaining life calculation unitor the display unitmay have a function of determining whether the remaining life value becomes smaller than the threshold value.

333 331 33 333 331 333 4 4 The replacement date calculation unitcalculates an estimated replacement date of the transmission mechanism based on the estimated life value of the transmission mechanism calculated by the life estimation unit. Accordingly, the life evaluation devicecan notify the operator of an appropriate replacement date of the transmission mechanism before the transmission mechanism breaks down. Specifically, the replacement date calculation unitcalculates a replacement date (recommended replacement date) of the transmission mechanism using Formula (9) below, based on the estimated life value of the transmission mechanism calculated by the life estimation unit. Information on the replacement date calculated by the replacement date calculation unitis sent to the display unitand displayed on the display unit. However, a method of calculating the replacement date of the transmission mechanism is not limited to Formula (9) below, and any other approximate calculation method may be adopted.

where, D: number of days until replacement date [days], q S(d): estimated life value of transmission mechanism until d day [%], g S(0): estimated life value of current transmission mechanism [%], g0 S: replacement line of remaining life [%], and a: coefficient.

33 32 33 32 As described above, the life evaluation devicecan accurately evaluate the life of the transmission mechanism, based on the estimated tension value of the belt obtained by the tension estimation device. Since the life evaluation deviceevaluates the life of the transmission mechanism based on the tension of the belt obtained by the tension estimation device, it is possible to evaluate the life with high accuracy in consideration of a load applied to the transmission mechanism due to the increase in the tension of the belt.

324 32 321 322 The belt tension estimation unitof the tension estimation devicemay generate a learned model for estimating the tension of the belt from the motor heating value and the friction heating value by machine learning using the motor heating value calculated by the motor heating value calculation unitand the friction heating value calculated by the friction heating value calculation unit. Accordingly, the tension of the belt can be estimated with high accuracy using a learned model based on various patterns of data on the motor heating value and the friction heating value.

324 32 325 324 325 325 4 FIG. When the belt tension estimation unitgenerates the learned model, the tension estimation devicemay include a storage unitthat stores the learned model generated by the machine learning, as shown in. In this case, the belt tension estimation unitcan estimate the tension of the belt using the learned model stored in the storage unitbased on the motor heating value and the friction heating value. Accordingly, since the tension of the belt is estimated using the learned model stored in the storage unit, the tension of the belt can be estimated with high accuracy even when the learned model is not generated from the beginning.

4 FIG. 35 3 The machine learning may be supervised learning using training data in which the motor heating value and the friction heating value used as input data are associated with the actually measured value of the tension of the belt used as a label. Accordingly, the actually measured value of the tension of the belt is used as a correct answer, and thus the tension of the belt with respect to the input data can be estimated with high accuracy. As shown in, the actually measured value of the tension of the belt is manually input by the operator through an actually measured value input unitprovided in the robot controller.

6 FIG. 5 FIG. 324 32 32 326 As shown in, the tension of the belt and the temperature have a one-to-one relationship. For this reason, the belt tension estimation unitof the tension estimation devicemay estimate the tension of the belt from the temperature of the transmission mechanism instead of calculating the estimated tension value of the belt using Formula (4) above. In this case, the tension estimation devicecan include a transmission mechanism temperature estimation unitas shown in.

326 321 322 323 The transmission mechanism temperature estimation unitestimates the temperature of the transmission mechanism using Formula (10) below, based on the motor heating value calculated by the motor heating value calculation unit, the friction heating value calculated by the friction heating value calculation unit, and the air-cooling radiation amount calculated by the air-cooling radiation amount calculation unit.

where, p T: estimated temperature of transmission mechanism, r T: room temperature, n F: friction heating value of axis to be driven by Jn axis motor [W], n M: motor heating value of Jn axis motor [W], 1 W: air-cooling radiation amount, 2 W: heating value of another generation source, a, b, c, d, e, f, g: coefficients, m: any combinatorial integer.

324 326 32 32 326 6 FIG. 4 FIG. The belt tension estimation unitestimates the tension of the belt from a graph of, based on the temperature of the transmission mechanism estimated by the transmission mechanism temperature estimation unit. Accordingly, the tension of the belt can be simply estimated. Similarly to the tension estimation deviceshown in, the tension estimation deviceincluding the transmission mechanism temperature estimation unitmay also have a configuration in which the learned model is generated by machine learning.

321 321 In each of the above-described embodiments, the motor heating value calculation unitcalculates the motor heating value based on the motor current value and the motor rotation speed. However, the motor heating value calculation unitmay more simply calculate the motor heating value based on at least one of the motor current value and the motor rotation speed.

322 6 6 322 6 6 In each of the above-described embodiments, the friction heating value calculation unitcalculates the friction heating value in the transmission mechanismbased on the motor current value, the motor rotation speed, and the friction coefficient of the transmission mechanism. However, the friction heating value calculation unitmay simply calculate the friction heating value in the transmission mechanismbased on at least one of the motor current value, the motor rotation speed, and the friction coefficient of the transmission mechanism.

32 323 324 In each of the above-described embodiments, the tension estimation devicemay be a simple device not including the air-cooling radiation amount calculation unit. Further, the belt tension estimation unitmay simply estimate the tension of the belt based on two heating values of the motor heating value and the friction heating value.

1 robot system 2 robot (machine) 2 a J1 axis (movable portion) 2 b J2 axis (movable portion) 2 c J3 axis (movable portion) 2 d J4 axis (movable portion) 2 e J5 axis (movable portion) 2 f J6 axis (movable portion) 31 control device 32 tension estimation device 321 motor heating value calculation unit 322 friction heating value calculation unit 324 belt tension estimation unit 323 air-cooling radiation amount calculation unit 325 storage unit 326 transmission mechanism temperature estimation unit 33 life evaluation device 331 life estimation unit 332 remaining life calculation unit 333 replacement date calculation unit 5 J5 axis motor (first motor) 7 J6 axis motor (second motor) 6 transmission mechanism 63 belt